This invention concerns a device for the axial clamping/release of the chocks of the rolls in a rolling mill stand.
To be more exact, the subject of this invention is embodied with a device which makes possible the quick and easy clamping and release, both on the working side and on the actuation side of the rolling mill stand, of the chocks bearing the working rolls to and from the relative sliding blocks providing axial displacement.
Moreover the device according to the invention makes possible a quick, easy and accurate connection and disconnection of the connectors feeding lubrication fluid to the bearings of the working rolls during the steps of changing the rolls.
The invention is applied advantageously, but not only, to rolling mill stands which process wide flat products and which require not only the normal reciprocal vertical positioning of the rolls but also a reciprocal axial displacement of the rolls so as to prevent hollows developing at given points in the circumference of the rolls owing to continuous wear.
Rolling mill stands have been disclosed which have their working rolls installed on chocks, which during working are secured axially to sliding blocks positioned between the chocks themselves and the stationary housings of the rolling mill stands.
Stationary blocks arranged axially to the rolls are generally included between the sliding blocks and the housings of the rolling mill stands.
Displacement means act on the sliding blocks and enable the working rolls to be displaced axially during the working steps.
The state of the art discloses various examples of systems of installation of the rolls on the relative chocks and of the chocks on the relative sliding blocks both on the actuation side and on the working side of the rolling mill stand, these systems ensuring a correct positioning of the rolls and the ability to obtain an accurate axial movement thereof.
JP-A-61-37307 discloses, for instance, a rolling mill stand in which the working rolls are associated with axial displacement means and in which an auxiliary thrust device is included which enables all the plays to be eliminated which are caused between the elements in reciprocal movement. This auxiliary device acts on the relative sliding block so as to ensure in an extremely accurate manner and under all operational conditions the correct desired axial displacement of the working rolls, thus obviating inaccuracies due to such plays.
SU-A-1,667,969 and SU-A-1,502,146 disclose a system for axial clamping of a chock to a relative sliding block, this system comprising an oscillatory lever element which can be momentarily disactivated during the step of changing the roll.
EP-A-483,599 discloses another example in which clamping lever means are included and are actuated, when the chock has been put in position, so as to clamp the chock axially to the sliding blocks.
One of the problems most often encountered in the state of the art arises from the modest size of the sliding blocks, or this size creates problems or the positioning of the sensors which monitor the open/closed positions or the lever elements.
The systems of the state of the art are therefore often devoid of the sensors, and this situation can entail problems of safety, control and speed of starting the working cycle of the rolling mill stand.
The sensors, when they are included, are positioned within the sliding blocks, with resulting problems during the step of acting on the sensors for cleaning, maintenance or replacement.
The problems linked to the changing of the working rolls are also found in this type of rolling stand. In fact, so as to change the rolls, it is necessary to release the chocks axially from the relative sliding blocks and to disconnect the connectors, which feed the lubricating fluid and which are included terminally and frontally on the chocks, from the connectors included on the machine.
During the step of fitting new rolls it is necessary first of all to align these connectors reciprocally and accurately so as to perform the coupling and then to secure the chocks axially to the sliding blocks.
A further problem is the fact that the chock during working has to be free to move also transversely to the sliding blocks, and this fact means also that the connectors included on the machine have to be able to follow the chock in its transverse movement.
This ability to make the connectors on the machine free to move transversely to the axis of the rolls entails problems of alignment and appropriate rotation of those connectors so that they will mate with the connectors on the chocks during the step of installation.
Moreover, the changing of the rolls has to be carried out in as short a time as possible so as not to involve long machine downtimes which could impair the output of the plant.
So as to avoid these problems and mainly to avoid the great losses of time due to the disconnection and successive connection of the lubricating connectors, it is the common practice in conventional rolling trains to use a grease lubrication system of a full fill-up type.
According to this lubrication system the bearings of the working rolls are filled with lubricating grease when the rolls are dismantled.
The rolls, when installed, are worked until the lubricating grease has been substantially all used up.
This lubricating system makes it possible not to have flexible connections on the machine and thus to eliminate the additional times and the alignment problems during installation which are due to the disconnection and successive re-connection of the hydraulic feeding connectors.
This system, however, is very expensive as compared to the centralised air-oil lubrication owing to the great quantity of lubricating grease which has to be employed. Moreover, it does not ensure a constant and balanced lubrication during the whole working cycle of the rolls.